In recent years, various developments have been made for an engine duct that is an essential structural element of an aircraft engine. A conventional engine duct according to a related art will briefly be explained in connection with its structure and the like.
The conventional engine duct has a cylindrical core cowl (an engine inner cylinder). Formed inside (on the inner side of) the core cowl is an annular core passage that takes in air and discharges a core jet. Arranged outside the core cowl is a cylindrical nacelle (engine outer cylinder) that surrounds the core cowl. Formed between an inner circumferential wall surface of the nacelle and an outer circumferential wall surface of the core cowl is an annular bypass passage that takes in air and discharges a bypass jet. In addition, arranged between the outer circumferential wall surface of the core cowl and the inner circumferential wall surface of the nacelle are a plurality of struts that are arranged at intervals in a circumferential direction to serve as structural members to support the nacelle with respect to the core cowl.
From an upper part of the core cowl to an upper part of the nacelle, a top pylon is integrally connected to serve as a main pylon that extends in parallel with an engine shaft direction of the aircraft engine. The top pylon projects upward (toward an outer side of a diametral direction) from the nacelle and is used to attach the aircraft engine to the aircraft and to transmit an engine thrust thereto. Set between a lower part of the outer circumferential wall surface of the core cowl and a lower part of the inner circumferential wall surface of the nacelle is a bottom pylon serving as a sub-pylon, the bottom pylon and top pylon being symmetrically set with respect to an engine shaft center. The bottom pylon is positioned between the struts that are adjacent to each other in the circumferential direction and has a function of serving as a structural member to support the nacelle with respect to the core cowl, and in addition, a function of accommodating piping and the like. Arranged between the outer circumferential wall surface of the core cowl and the inner circumferential wall surface of the nacelle upstream from the struts are a plurality of fan outlet guide vanes that are arranged at intervals in the circumferential direction to rectify the air taken into the bypass passage into an axial flow.
When the aircraft engine is started, air taken into the core passage is discharged as a core jet and air taken into the bypass passage is rectified into an axial flow and discharged as a bypass jet. This results in generating an engine thrust of the aircraft engine.
Related arts concerning the present invention include Japanese Unexamined Patent Application Publication No. 2008-151033 (Patent Literature 1) and Japanese Unexamined Patent Application Publication No. H05-202768 (Patent Literature 2).